This invention relates to turbocharger apparatus and it relates more especially to variable turbocharger apparatus.
Different types of turbocharger apparatus are known. One known type of turbocharger apparatus comprises a housing, a compressor mounted for rotation in the housing, a turbine mounted for rotation in the housing, a first inlet for enabling air to be conducted to the compressor, an outlet for air from the compressor, a second inlet for enabling exhaust gases from an engine to be conducted to the turbine, and a chamber which surrounds the turbine and which receives the exhaust gases from the second inlet before the exhaust gases are conducted to the turbine. This known type of turbocharger apparatus is such that there is a fixed gap through which the exhaust gases in the chamber can pass to the turbine. The size of this gap is chosen to be a compromise between the various different sizes of gap that are ideally required for different engine operating conditions. This means that, for most engine operating conditions, the gap is not exactly correct and the turbocharger apparatus thus operates at less than its optimum performance. For example, with a relatively small gap, the turbocharger apparatus gives a quick response but excessive pressure tends to build up in the chamber. With a large gap, the build up of excessive pressure in the chamber is avoided but then the response time of the turbine apparatus is slow.